1. Field of the Invention
The present invention generally relates to the manufacture of semiconductor devices and more particularly to multiple beam electron beam lithography.
2. Description of the Related Art
Lithography systems are used for creating patterns, such as features of an electronic circuit, on a semiconductor substrate. In one type of suggested electron beam lithography system, a light beam from a light source is demagnified and focused on a photocathode, which then converts the light beam into an electron beam (see, for example, U.S. Pat. No. 4,820,927 to Langner et al.). By modulating the light source and by scanning the electron beam using an electron optics, a desired pattern can be written on a mask blank (for later photolithography) or directly on a semiconductor substrate (direct-write lithography). In this disclosure, the term xe2x80x9cwriting planexe2x80x9d includes semiconductor substrates, lithography mask blanks, and like workpieces.
A multiple beam electron beam lithography system (xe2x80x9cmulti-beam systemxe2x80x9d) works similarly as described above except that multiple light sources are employed (see, for example, U.S. Pat. No. 5,039,862 to Smith et al. and U.S. Pat. No. 5,684,360 to Baum et al.). The light sources are typically arranged in an array and individually modulated to create the pattern. The placement of the light sources relative to one another in the array is critical in a multi-beam system because a light source placement error directly translates to an electron beam writing error. In the fabrication of 0.1 micrometer devices, for example, electron beam writing errors less than 10 nm are required. Further, the rate at which the light sources are modulated to create the pattern affects the throughput of the multi-beam system. It is desirable to increase the modulation rate of the light sources to achieve a corresponding increase in the number of writing planes that can be processed.
The photocathode and electron optics of a multi-beam system are typically contained in an evacuated electron beam column. It is desirable to shorten the length of the column to reduce interaction between electrons (xe2x80x9celectron-electron interactionxe2x80x9d) in an electron beam. Electron-electron interaction blurs the electron beam, thereby degrading the resolution of the pattern written on the writing plane. It is also desirable to shorten the length of the column to simplify its design.
The present invention relates to a multiple beam electron beam lithography system. In one embodiment, an array of vertical cavity surface emitting lasers (VCSELs) generates laser beams, which are then converted to electron beams using a photocathode. The electron beams are scanned across a writing plane to image a pattern thereon. The VCSELs are electronically modulated using circuitry located outside the electron beam column. The use of VCSELs simplifies the design of the electron beam column and improves the writing resolution and throughput of the lithography system.
Other features and advantages of the present invention will be apparent to one of ordinary skill in the art upon reading the following description, figures, and claims.